Keeling Curve

Beginning in 1958, the American scientist Charles David Keeling established continuous, high-precision measurements of atmospheric carbon dioxide concentration at the Mauna Loa Observatory in Hawaii, chosen for its high altitude and distance from major local sources of pollution that could distort readings. The resulting record, known as the Keeling Curve, revealed both a small seasonal oscillation driven by the growth and die-back of Northern Hemisphere vegetation and a steady year-on-year rise in carbon dioxide concentration, providing the first unambiguous, continuously measured evidence that atmospheric carbon dioxide was increasing as a result of human activity. The measurements have continued essentially unbroken since 1958 and remain the longest direct record of atmospheric carbon dioxide, foundational to the modern scientific understanding of human-driven climate change.